Fundament - not so known stuff

mbuf tags
capability to tag packets inside the network stack
tag incomming packets, check later
used by ipsec and various loop prevention mechanisms
rtlabels
pf, bgpd, ospfd and ripd support route labels.
pf can filter or tag traffic based on rtlabels.
bgpd can tag routes based on route labels.
ripd and ospfd can redistribute routes based on their label.
carp demotion counter
Demotion of a carp interface from userland.
The counter can be increased in case an important part of the system fails (partial failure)
a less degraded system becomes master
independent of advskew